The present invention relates to phosphate ester compounds containing terminal vicinal epoxide functionality, and a process for the preparation of these compounds. More particularly, the present invention relates to hydrolytically stable compositions of matter comprising the reaction product of an epoxide, such as a diglycidyl ether of a dihydroxy compound, and a phosphoric acid ester. The compositions are readily cured by known epoxy curing agents such as amines and anhydrides to form coatings and cast articles. The cured compositions of the present invention are highly useful due to their ability to form char upon application of heat, thereby finding use in intumescent paints and in ablative coatings. Accordingly, a further species of the present invention is an intumescent coating comprising the above phosphate ester compounds containing terminal vicinal epoxide functionality. Said intumescent coatings exhibit improved adhesion to metal and glass substrates.
In U.S. Pat. No. 2,541,027, cured coatings are prepared by the reaction of epoxy ethers such as the diglycidyl ether of bisphenol A with orthophosphoric acid or a monoalkyl orthophosphate. The curing reaction was initiated by mixing together the epoxy resin and the phosphorus-containing curing agent and heating the resulting mixture at an elevated temperature to totally eliminate all epoxide functionality.
In U.S. Pat. No. 4,256,844; 4,289,812; 4,164,487; and 4,316,922, additional adducts of phosphoric acid and epoxides that form water-dispersible neutralized adducts are described. In each reference, the epoxide functionality is completely ring-opened thereby forming secondary hydroxyl-containing compositions. Curing such ring-opened compositions was effected by reaction with hydroxyl curing agents such as isocyanates.
In U.S. Pat. No. 4,425,451, monoesters of orthophosphoric acid and epoxy ethers such as the diglycidyl ether of bisphenol A were prepared by reaction of the ether with 85 percent orthophosphoric acid (in water) in the presence of 2-butoxyethanol solvent. Residual phosphoric acid functionality was neutralized by salification with an amine.
The presence of reactive phosphoric acid moieties in previously known processes has resulted disadvantageously in the formation of various cyclic phosphorus-containing epoxy functionalized esters of phosphoric acid. See U.S. Pat. No. 3,639,545 and 3,652,743. In addition, it has been found that gelling of the resin results by means of reaction between phosphoric acid functionality and epoxide thereby resulting in a loss of epoxide values over time.
In view of the deficiencies of the prior art processes, it would be desirable to provide a process for effectively preparing epoxy derivatives of monoesters of phosphoric acid in high yields. Additionally, it would be desirable to provide a process for preparing epoxy derivatives of phosphoric acid esters that are relatively unaffected by epoxide degradation during storage.